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package java.nio.file;

import java.nio.file.attribute.*;
import java.nio.file.spi.FileSystemProvider;
import java.util.Set;
import java.io.Closeable;
import java.io.IOException;

/**
 * Provides an interface to a file system and is the factory for objects to
 * access files and other objects in the file system.
 *
 * <p> The default file system, obtained by invoking the {@link FileSystems#getDefault
 * FileSystems.getDefault} method, provides access to the file system that is
 * accessible to the Java virtual machine. The {@link FileSystems} class defines
 * methods to create file systems that provide access to other types of (custom)
 * file systems.
 *
 * <p> A file system is the factory for several types of objects:
 *
 * <ul>
 * <li><p> The {@link #getPath getPath} method converts a system dependent
 * <em>path string</em>, returning a {@link Path} object that may be used
 * to locate and access a file. </p></li>
 * <li><p> The {@link #getPathMatcher  getPathMatcher} method is used
 * to create a {@link PathMatcher} that performs match operations on
 * paths. </p></li>
 * <li><p> The {@link #getFileStores getFileStores} method returns an iterator
 * over the underlying {@link FileStore file-stores}. </p></li>
 * <li><p> The {@link #getUserPrincipalLookupService getUserPrincipalLookupService}
 * method returns the {@link UserPrincipalLookupService} to lookup users or
 * groups by name. </p></li>
 * <li><p> The {@link #newWatchService newWatchService} method creates a
 * {@link WatchService} that may be used to watch objects for changes and
 * events. </p></li>
 * </ul>
 *
 * <p> File systems vary greatly. In some cases the file system is a single
 * hierarchy of files with one top-level root directory. In other cases it may
 * have several distinct file hierarchies, each with its own top-level root
 * directory. The {@link #getRootDirectories getRootDirectories} method may be
 * used to iterate over the root directories in the file system. A file system
 * is typically composed of one or more underlying {@link FileStore file-stores}
 * that provide the storage for the files. Theses file stores can also vary in
 * the features they support, and the file attributes or <em>meta-data</em> that
 * they associate with files.
 *
 * <p> A file system is open upon creation and can be closed by invoking its
 * {@link #close() close} method. Once closed, any further attempt to access
 * objects in the file system cause {@link ClosedFileSystemException} to be
 * thrown. File systems created by the default {@link FileSystemProvider provider}
 * cannot be closed.
 *
 * <p> A {@code FileSystem} can provide read-only or read-write access to the
 * file system. Whether or not a file system provides read-only access is
 * established when the {@code FileSystem} is created and can be tested by invoking
 * its {@link #isReadOnly() isReadOnly} method. Attempts to write to file stores
 * by means of an object associated with a read-only file system throws {@link
 * ReadOnlyFileSystemException}.
 *
 * <p> File systems are safe for use by multiple concurrent threads. The {@link
 * #close close} method may be invoked at any time to close a file system but
 * whether a file system is <i>asynchronously closeable</i> is provider specific
 * and therefore unspecified. In other words, if a thread is accessing an
 * object in a file system, and another thread invokes the {@code close} method
 * then it may require to block until the first operation is complete. Closing
 * a file system causes all open channels, watch services, and other {@link
 * Closeable closeable} objects associated with the file system to be closed.
 *
 * @since 1.7
 */

public abstract class FileSystem
    implements Closeable {

  /**
   * Initializes a new instance of this class.
   */
  protected FileSystem() {
  }

  /**
   * Returns the provider that created this file system.
   *
   * @return The provider that created this file system.
   */
  public abstract FileSystemProvider provider();

  /**
   * Closes this file system.
   *
   * <p> After a file system is closed then all subsequent access to the file
   * system, either by methods defined by this class or on objects associated
   * with this file system, throw {@link ClosedFileSystemException}. If the
   * file system is already closed then invoking this method has no effect.
   *
   * <p> Closing a file system will close all open {@link
   * java.nio.channels.Channel channels}, {@link DirectoryStream directory-streams},
   * {@link WatchService watch-service}, and other closeable objects associated
   * with this file system. The {@link FileSystems#getDefault default} file
   * system cannot be closed.
   *
   * @throws IOException If an I/O error occurs
   * @throws UnsupportedOperationException Thrown in the case of the default file system
   */
  @Override
  public abstract void close() throws IOException;

  /**
   * Tells whether or not this file system is open.
   *
   * <p> File systems created by the default provider are always open.
   *
   * @return {@code true} if, and only if, this file system is open
   */
  public abstract boolean isOpen();

  /**
   * Tells whether or not this file system allows only read-only access to
   * its file stores.
   *
   * @return {@code true} if, and only if, this file system provides read-only access
   */
  public abstract boolean isReadOnly();

  /**
   * Returns the name separator, represented as a string.
   *
   * <p> The name separator is used to separate names in a path string. An
   * implementation may support multiple name separators in which case this
   * method returns an implementation specific <em>default</em> name separator.
   * This separator is used when creating path strings by invoking the {@link
   * Path#toString() toString()} method.
   *
   * <p> In the case of the default provider, this method returns the same
   * separator as {@link java.io.File#separator}.
   *
   * @return The name separator
   */
  public abstract String getSeparator();

  /**
   * Returns an object to iterate over the paths of the root directories.
   *
   * <p> A file system provides access to a file store that may be composed
   * of a number of distinct file hierarchies, each with its own top-level
   * root directory. Unless denied by the security manager, each element in
   * the returned iterator corresponds to the root directory of a distinct
   * file hierarchy. The order of the elements is not defined. The file
   * hierarchies may change during the lifetime of the Java virtual machine.
   * For example, in some implementations, the insertion of removable media
   * may result in the creation of a new file hierarchy with its own
   * top-level directory.
   *
   * <p> When a security manager is installed, it is invoked to check access
   * to the each root directory. If denied, the root directory is not returned
   * by the iterator. In the case of the default provider, the {@link
   * SecurityManager#checkRead(String)} method is invoked to check read access
   * to each root directory. It is system dependent if the permission checks
   * are done when the iterator is obtained or during iteration.
   *
   * @return An object to iterate over the root directories
   */
  public abstract Iterable<Path> getRootDirectories();

  /**
   * Returns an object to iterate over the underlying file stores.
   *
   * <p> The elements of the returned iterator are the {@link
   * FileStore FileStores} for this file system. The order of the elements is
   * not defined and the file stores may change during the lifetime of the
   * Java virtual machine. When an I/O error occurs, perhaps because a file
   * store is not accessible, then it is not returned by the iterator.
   *
   * <p> In the case of the default provider, and a security manager is
   * installed, the security manager is invoked to check {@link
   * RuntimePermission}<tt>("getFileStoreAttributes")</tt>. If denied, then
   * no file stores are returned by the iterator. In addition, the security
   * manager's {@link SecurityManager#checkRead(String)} method is invoked to
   * check read access to the file store's <em>top-most</em> directory. If
   * denied, the file store is not returned by the iterator. It is system
   * dependent if the permission checks are done when the iterator is obtained
   * or during iteration.
   *
   * <p> <b>Usage Example:</b>
   * Suppose we want to print the space usage for all file stores:
   * <pre>
   *     for (FileStore store: FileSystems.getDefault().getFileStores()) {
   *         long total = store.getTotalSpace() / 1024;
   *         long used = (store.getTotalSpace() - store.getUnallocatedSpace()) / 1024;
   *         long avail = store.getUsableSpace() / 1024;
   *         System.out.format("%-20s %12d %12d %12d%n", store, total, used, avail);
   *     }
   * </pre>
   *
   * @return An object to iterate over the backing file stores
   */
  public abstract Iterable<FileStore> getFileStores();

  /**
   * Returns the set of the {@link FileAttributeView#name names} of the file
   * attribute views supported by this {@code FileSystem}.
   *
   * <p> The {@link BasicFileAttributeView} is required to be supported and
   * therefore the set contains at least one element, "basic".
   *
   * <p> The {@link FileStore#supportsFileAttributeView(String)
   * supportsFileAttributeView(String)} method may be used to test if an
   * underlying {@link FileStore} supports the file attributes identified by a
   * file attribute view.
   *
   * @return An unmodifiable set of the names of the supported file attribute views
   */
  public abstract Set<String> supportedFileAttributeViews();

  /**
   * Converts a path string, or a sequence of strings that when joined form
   * a path string, to a {@code Path}. If {@code more} does not specify any
   * elements then the value of the {@code first} parameter is the path string
   * to convert. If {@code more} specifies one or more elements then each
   * non-empty string, including {@code first}, is considered to be a sequence
   * of name elements (see {@link Path}) and is joined to form a path string.
   * The details as to how the Strings are joined is provider specific but
   * typically they will be joined using the {@link #getSeparator
   * name-separator} as the separator. For example, if the name separator is
   * "{@code /}" and {@code getPath("/foo","bar","gus")} is invoked, then the
   * path string {@code "/foo/bar/gus"} is converted to a {@code Path}.
   * A {@code Path} representing an empty path is returned if {@code first}
   * is the empty string and {@code more} does not contain any non-empty
   * strings.
   *
   * <p> The parsing and conversion to a path object is inherently
   * implementation dependent. In the simplest case, the path string is rejected,
   * and {@link InvalidPathException} thrown, if the path string contains
   * characters that cannot be converted to characters that are <em>legal</em>
   * to the file store. For example, on UNIX systems, the NUL (&#92;u0000)
   * character is not allowed to be present in a path. An implementation may
   * choose to reject path strings that contain names that are longer than those
   * allowed by any file store, and where an implementation supports a complex
   * path syntax, it may choose to reject path strings that are <em>badly
   * formed</em>.
   *
   * <p> In the case of the default provider, path strings are parsed based
   * on the definition of paths at the platform or virtual file system level.
   * For example, an operating system may not allow specific characters to be
   * present in a file name, but a specific underlying file store may impose
   * different or additional restrictions on the set of legal
   * characters.
   *
   * <p> This method throws {@link InvalidPathException} when the path string
   * cannot be converted to a path. Where possible, and where applicable,
   * the exception is created with an {@link InvalidPathException#getIndex
   * index} value indicating the first position in the {@code path} parameter
   * that caused the path string to be rejected.
   *
   * @param first the path string or initial part of the path string
   * @param more additional strings to be joined to form the path string
   * @return the resulting {@code Path}
   * @throws InvalidPathException If the path string cannot be converted
   */
  public abstract Path getPath(String first, String... more);

  /**
   * Returns a {@code PathMatcher} that performs match operations on the
   * {@code String} representation of {@link Path} objects by interpreting a
   * given pattern.
   *
   * The {@code syntaxAndPattern} parameter identifies the syntax and the
   * pattern and takes the form:
   * <blockquote><pre>
   * <i>syntax</i><b>:</b><i>pattern</i>
   * </pre></blockquote>
   * where {@code ':'} stands for itself.
   *
   * <p> A {@code FileSystem} implementation supports the "{@code glob}" and
   * "{@code regex}" syntaxes, and may support others. The value of the syntax
   * component is compared without regard to case.
   *
   * <p> When the syntax is "{@code glob}" then the {@code String}
   * representation of the path is matched using a limited pattern language
   * that resembles regular expressions but with a simpler syntax. For example:
   *
   * <blockquote>
   * <table border="0" summary="Pattern Language">
   * <tr>
   * <td>{@code *.java}</td>
   * <td>Matches a path that represents a file name ending in {@code .java}</td>
   * </tr>
   * <tr>
   * <td>{@code *.*}</td>
   * <td>Matches file names containing a dot</td>
   * </tr>
   * <tr>
   * <td>{@code *.{java,class}}</td>
   * <td>Matches file names ending with {@code .java} or {@code .class}</td>
   * </tr>
   * <tr>
   * <td>{@code foo.?}</td>
   * <td>Matches file names starting with {@code foo.} and a single
   * character extension</td>
   * </tr>
   * <tr>
   * <td><tt>&#47;home&#47;*&#47;*</tt>
   * <td>Matches <tt>&#47;home&#47;gus&#47;data</tt> on UNIX platforms</td>
   * </tr>
   * <tr>
   * <td><tt>&#47;home&#47;**</tt>
   * <td>Matches <tt>&#47;home&#47;gus</tt> and
   * <tt>&#47;home&#47;gus&#47;data</tt> on UNIX platforms</td>
   * </tr>
   * <tr>
   * <td><tt>C:&#92;&#92;*</tt>
   * <td>Matches <tt>C:&#92;foo</tt> and <tt>C:&#92;bar</tt> on the Windows
   * platform (note that the backslash is escaped; as a string literal in the
   * Java Language the pattern would be <tt>"C:&#92;&#92;&#92;&#92;*"</tt>) </td>
   * </tr>
   *
   * </table>
   * </blockquote>
   *
   * <p> The following rules are used to interpret glob patterns:
   *
   * <ul>
   * <li><p> The {@code *} character matches zero or more {@link Character
   * characters} of a {@link Path#getName(int) name} component without
   * crossing directory boundaries. </p></li>
   *
   * <li><p> The {@code **} characters matches zero or more {@link Character
   * characters} crossing directory boundaries. </p></li>
   *
   * <li><p> The {@code ?} character matches exactly one character of a
   * name component.</p></li>
   *
   * <li><p> The backslash character ({@code \}) is used to escape characters
   * that would otherwise be interpreted as special characters. The expression
   * {@code \\} matches a single backslash and "\{" matches a left brace
   * for example.  </p></li>
   *
   * <li><p> The {@code [ ]} characters are a <i>bracket expression</i> that
   * match a single character of a name component out of a set of characters.
   * For example, {@code [abc]} matches {@code "a"}, {@code "b"}, or {@code "c"}.
   * The hyphen ({@code -}) may be used to specify a range so {@code [a-z]}
   * specifies a range that matches from {@code "a"} to {@code "z"} (inclusive).
   * These forms can be mixed so [abce-g] matches {@code "a"}, {@code "b"},
   * {@code "c"}, {@code "e"}, {@code "f"} or {@code "g"}. If the character
   * after the {@code [} is a {@code !} then it is used for negation so {@code
   * [!a-c]} matches any character except {@code "a"}, {@code "b"}, or {@code
   * "c"}.
   * <p> Within a bracket expression the {@code *}, {@code ?} and {@code \}
   * characters match themselves. The ({@code -}) character matches itself if
   * it is the first character within the brackets, or the first character
   * after the {@code !} if negating.</p></li>
   *
   * <li><p> The {@code { }} characters are a group of subpatterns, where
   * the group matches if any subpattern in the group matches. The {@code ","}
   * character is used to separate the subpatterns. Groups cannot be nested.
   * </p></li>
   *
   * <li><p> Leading period<tt>&#47;</tt>dot characters in file name are
   * treated as regular characters in match operations. For example,
   * the {@code "*"} glob pattern matches file name {@code ".login"}.
   * The {@link Files#isHidden} method may be used to test whether a file
   * is considered hidden.
   * </p></li>
   *
   * <li><p> All other characters match themselves in an implementation
   * dependent manner. This includes characters representing any {@link
   * FileSystem#getSeparator name-separators}. </p></li>
   *
   * <li><p> The matching of {@link Path#getRoot root} components is highly
   * implementation-dependent and is not specified. </p></li>
   *
   * </ul>
   *
   * <p> When the syntax is "{@code regex}" then the pattern component is a
   * regular expression as defined by the {@link java.util.regex.Pattern}
   * class.
   *
   * <p>  For both the glob and regex syntaxes, the matching details, such as
   * whether the matching is case sensitive, are implementation-dependent
   * and therefore not specified.
   *
   * @param syntaxAndPattern The syntax and pattern
   * @return A path matcher that may be used to match paths against the pattern
   * @throws IllegalArgumentException If the parameter does not take the form: {@code
   * syntax:pattern}
   * @throws java.util.regex.PatternSyntaxException If the pattern is invalid
   * @throws UnsupportedOperationException If the pattern syntax is not known to the implementation
   * @see Files#newDirectoryStream(Path, String)
   */
  public abstract PathMatcher getPathMatcher(String syntaxAndPattern);

  /**
   * Returns the {@code UserPrincipalLookupService} for this file system <i>(optional
   * operation)</i>. The resulting lookup service may be used to lookup user or group names.
   *
   * <p> <b>Usage Example:</b> Suppose we want to make "joe" the owner of a file:
   * <pre>
   *     UserPrincipalLookupService lookupService = FileSystems.getDefault().getUserPrincipalLookupService();
   *     Files.setOwner(path, lookupService.lookupPrincipalByName("joe"));
   * </pre>
   *
   * @return The {@code UserPrincipalLookupService} for this file system
   * @throws UnsupportedOperationException If this {@code FileSystem} does not does have a lookup
   * service
   */
  public abstract UserPrincipalLookupService getUserPrincipalLookupService();

  /**
   * Constructs a new {@link WatchService} <i>(optional operation)</i>.
   *
   * <p> This method constructs a new watch service that may be used to watch
   * registered objects for changes and events.
   *
   * @return a new watch service
   * @throws UnsupportedOperationException If this {@code FileSystem} does not support watching file
   * system objects for changes and events. This exception is not thrown by {@code FileSystems}
   * created by the default provider.
   * @throws IOException If an I/O error occurs
   */
  public abstract WatchService newWatchService() throws IOException;
}
